The presently disclosed embodiments are directed to the field of automotive components, and particularly, controlling the microstructure of regions within such components by use of particular hot stamping processes.
It is well known in the art to selectively heat treat vehicle components to impart desired characteristics to certain portions or regions of the component. For example, it is known to selectively heat a side intrusion door beam. Select portions of the beam may be heat treated to modify the load characteristics of the beam.
It is also known to selectively cool or quench in order to harden regions of vehicle components such as bumpers. Such components can be formed to exhibit improved strength from selective austenitic-martensitic hardening. Bumpers can be formed by stamping a bumper blank from sheet steel, forming the desired shape, and then hardening select portions of the shape by heating and cooling.
High strength door beams have also been produced. Such door beams are subjected to heating and quenching operations to impart high strength characteristics. End flanges attached to the door beam are not affected by the operations, and so can be readily shaped and welded.
It is also known to cold form a vehicle component, such as an impact beam, followed by heating the component in select regions and then quenching, to strengthened portions of the component.
Although satisfactory in many regards, these prior strategies for forming vehicle components utilize multiple operations which typically require additional manufacturing time, floor space, and capital expenditures.
Hot stamping processes are also known. The terms “hot stamping,” “press hardening,” or “die hardening” as referenced in Europe, refer to a stamping operation in which forming and quenching operations are performed in a single step. An article was recently published regarding this technique, Merklein et al., “Investigation of the Thermo-mechanical Properties of Hot Stamping Steels,” Journal of Materials Processing Technology, 177 (2006), 452-455. Additionally, a three part collection of articles appearing in the Stamping Journal from December, 2006 through February, 2007 described hot stamping in the production of automotive components. These articles described forming complex, crash-resistant parts such as bumpers and pillars with ultra high strength, minimum spring back, and reduced sheet thickness. Various hot stamping processes are also generally referenced in the patent literature.
As design of automotive components becomes increasingly sophisticated, it is frequently desirable to produce a steel component having different physical characteristics in different regions of the component. As far as is known, hot stamping processes have been directed to the entirety of a steel member. And so, if it were desired to produce an engineered steel component with different physical characteristics at different regions of the component, it was generally not feasible to use currently known hot stamping processes.
Accordingly, a need remains in the art for an improved strategy for forming vehicle components by a hot stamping process, and particularly, one in which different regions of the components can be produced so as to exhibit different physical characteristics in those regions. Furthermore, it would be desirable to provide one or more hot stamping operations that enable the formation of vehicle components having regions with selective strength characteristics.